The use of endovascular techniques for the occlusion of body cavities such as arteries, veins, fallopian tubes or vascular deformities such as for example vascular aneurysms is known in the art. The occlusion spiral is in this case usually introduced with the aid of an endovascular guide wire through a catheter into the cavity to be occluded and deposited therein.
The severance of the occluding spiral necessary for deposit thereof is in particular technically problematical, since the device required must on the one hand be as small as possible in design in order to be guided through the fine bore of the catheter to its destination, while on the other hand it must bring about a reliable severance of the occluding spiral, since otherwise on withdrawal of the catheter there might be an unintended removal of the occluding spiral from the cavity to be occluded and thus injury and/or rupture of the wall of the cavity or vessel.
Mechanical methods for the severance of occluding spirals from the insertion means do not take much time to perform but however the rigidity necessitated by technical features of the connection means between the occluding spiral and the introduction means impede the introduction of the implant. Furthermore, the low load carrying capacity of the connection due to its rigidity entails a not inappreciable risk of premature detachment of the insertion means from the occluding implant. Moreover, in the case of mechanical separation of the inserting wire and the occluding spiral, energy must be transmitted (as a rule by rotation of the inserting wire) and this may mean that the implant is dislodged out of the correct position.
The electrolytic severance of stainless steel wire ends during transcatheter electro-coagulation of blood vessels or deformities of the same was initially described in 1979 by Thompson et al. and by McAlister et al. (Radiology 133: 335-340, November 1979, AJR 132: 998-1000, June 1979).
Based on this method the European patent publication 0 484 468 described an occluding spiral involving the electrolytically corrodible design of the end of the guide wire at the connection between the guide wire and the occluding spiral. Although this device elegantly makes use of the voltage, applied to the occluding spiral serving as an anode for electro-thrombization, for the simultaneous severance of the wire end and the occluding spiral thereon, it does, just like the above mentioned mechanical severance method, suffer from the disadvantage that only implants of predetermined length can be detached or severed. It is therefore as a rule generally necessary for the length, that is to say the longitudinal extent, of the occluding spiral to be inserted, to be predetermined directly prior to the insertion of the implant on the basis of the size of the cavity to be occluded. Since the irregular form of body cavities to be occluded makes it difficult to correctly assess the length of the occluding spiral necessary for filling, there is the likelihood of excessively long or excessively short occluding spirals being introduced into the cavity to be occluded, something which may involve on the one hand an incomplete occlusion or on the other hand injury to or rupture of the wall of the cavity (or of contiguous vessels) to be occluded.
A further disadvantage of the electrolytic severance of the end of the guide wire is the fact that for production of the guide wire the only materials which can be utilized are those, which have a sufficiently high degree of strength to enable reliable guidance of the occluding wire through the guide wire. The selection of materials for forming the point of eventual electrolytic severance is consequently extremely limited.
In the case of prior art devices for the electrolytic severance of occluding spirals the latter and the guide wire are not produced integrally, but as a rule mechanically connected with each other. This design has the inherent disadvantage that in order to ensure sufficient strength in the proximal zone of the guide wire and for the purpose of rendering possible the electrolytic, corrosive severance of the wire end in the distal part of the wire the guide wire must be tapered toward its end in an involved grinding operation. This corrodible zone of the end of the guide wire at the connection between the guide wire and the occluding spiral must not, in order to ensure sufficient strength of the connection point, have a diameter below a certain minimum value of approximately 0.05 mm, since it is subjected to a high flexural load. The corrodible wire end representing the connection point between the occluding spiral and the guide wire is consequently extremely rigid and requires a relatively long time for electrolytic corrosive severance.
The German patent publication 4,445,715 C2 describes the severance of an occluding spiral from the insertion means by means of a laser beam directed or focussed on the point of severance of the implant using an entrained fiber light guide. This device renders possible severance of an optimum length of the occluding spiral in the course of an operation as needed for filling the cavity. Thus even in the case of the use of occluding spirals of uniform length this method renders possible the severance and deposit of a the length best suited for filling the cavity. The technology necessary for the application of this device is however presently extremely expensive.